The blood-brain barrier (BBB), which normally restricts the entry of diverse tracer substances into the brain parenchyma, is an expression of the unique structure of the endothelial cells lining the cerebral microvessels; these cells are joined by tightly sealed intercellular junctions, and contain sparse pinocytotic vesicles and no fenestrae. Vasogenic brain edema is characterized by a breakdown in the BBB associated with intense pinocytosis and vesicular transport of blood-borne macromolecules into white matter. The factors that regulate this abnormal pinocytotic activity are largely unknown. This project will investigate the molecular pathology of the cerebral microvessels after freezing injury and after intracarotid infusion of a hyperosmolar mannitol solution with the object of delineating the factor(s) that regulate pinocytosis and enhanced endothelial cell permeability. We hypothesize that an adematogenic insult releases a pinocytosis-inducing factor which initiates a cascade of membrane reactions at the luminal surface that includes increased calcium transport, prostaglandin synthesis and cAMP, and is followed by an induction of ornithine decarboxylase (ODC) and an accumulation of polyamines. The polyamines release free cytoplasmic Ca2+ from calcium storage depots with in turn promotes pinocytosis (and other Ca2+-dependent processes). The goals of this project are: (1) to correlate time course changes in ODC and polyamine levels in isolated cerebral microvessels and brain parenchyma with changes in BBB permeability; (2) to assess the importance of polyamine synthesis with the aid of specific ODC inhibitor, Alpha-difluoromethylornithine (DFMO); (3) to investigate the moledular mechanism of action of dexamethasone in attenuating vasogenic edema; and to explore the potential use of aspirin and verapamil to suppress BBB breakdown and to influence polyamine synthesis.